Dieter Bohn explains how Twiiter's new cards send users directly into mobile apps, completely avoiding The Web:

Interestingly, Twitter's cards theoretically cut out the larger web from the loop for mobile users, allowing them to jump from app to app directly rather than jumping out to a web browser.

Flickr is reportedly happy to be on board and Path has already detailed how its integration will work

Few were hoping that Twitter would be announcing some kind of reversal of its increasingly restrictive APIs for third party apps, and that definitely didn't happen. CEO Dick Costolo said last year that he prefers that developers "build into Twitter" instead of "build off Twitter," and that walled-garden philosophy is still in full effect. That philosophy cuts both ways: despite the new options for developers, it's unlikely that Instagram will change its mind and take advantage of the new Cards.

In the mobile apps vs The Web debate, mobile apps just got a boost from Twitter.